Traditional fisheries management is the best way to manage weak stocks.

Hastings et al. (1) model a fishery with a weak and a strong stock. Using several examples from the US West Coast they conclude that marine protected areas (MPAs) are an effective way to allow harvest of strong stock while allowing for persistence of weak stocks and that MPAs have distinct advantages over traditional fisheries management. I constructed a model similar to theirs, except my model includes full age structure and also measures required fishing effort (2). I used a strong stock whose yield is maximized at 26% harvest per year and a weak stock which would be extinct at that rate and whose yield is maximized at a 5% harvest per year and defined persistence of the weak stock as its steady-state abundance at 20% of its unfished abundance. I found a result similar to theirs: With 33% of the total area in reserves the yield could be increased from the noreserve case by 61%. However, to achieve those yields the total fishing effort needed to be 19 times higher than the fishing effort that maximized strong-stock yield and weakstock protection with no reserves. The MPA solution they proposed has fishing mortality outside of the reserves very high and the fishery essentially subsists on new recruits as larvae settle from the spawning inside the reserves. This is neither economically practical nor ecologically desirable. A bit more reasonable solution occurs with 30% of the area in reserve, which provides for a 47% increase in yield for a 3.1-fold increase in effort. Inmost mixed-stock fisheries a threefold increase in effort is economically unrealistic. Hastings et al. (1) do not include any measure of fishing effort required. Hastings et al. (1) assume that the weak and strong stocks had the same exploitation rate, but this is simply not true (3). The weak stocks on the West Coast of the United States are four rockfish species that have been under rebuilding plans and have very low allowable catches. The annual exploitation rate for these rockfish was 0.46% in 2012, whereas other rockfish were harvested at 3%, over five times higher (from individual assessments in www.pcouncil.org/topic/ groundfish/.) These differences in exploitation rate were achieved because the spatial distribution of strong and weak stocks is not uniform as assumed by Hastings et al. (1), but there are large-scale and smallscale differences in distribution that managers and fishermen can exploit. For instance, managers closed some areas known as “rockfish conservation areas” to the kind of fishing gear used to target rockfish, and fishermen were given individual quotas for each species. Many fishermen formed cooperatives to share information about where weak stocks were found and mutually agreed not to fish in those areas. If we assume weak stocks have one-third the exploitation rate of strong stocks, then the best strong-stock yield subject to protecting the weak stock is achieved without MPAs. Thus, we suggest that in fact traditional fisheries management measures are a more effective way to protect weak stocks than MPAs.